<html>
 <head>
  <link href="./leetcode-problem.css" rel="stylesheet" type="text/css">
 </head>
 <body>
  <div class="question_difficulty">
   难度：Easy
  </div>
  <div>
   <h1 class="question_title">
    637. Average of Levels in Binary Tree
   </h1>
   Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.
   <p>
    <b>
     Example 1:
    </b>
    <br>
   </p>
   <pre>
<b>Input:</b>
    3
   / \
  9  20
    /  \
   15   7
<b>Output:</b> [3, 14.5, 11]
<b>Explanation:</b>
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].
</pre>
   <p>
    <b>
     Note:
    </b>
    <br>
   </p>
   <ol>
    <li>
     The range of node's value is in the range of 32-bit signed integer.
    </li>
   </ol>
  </div>
  <div>
   <h1 class="question_title">
    637. 二叉树的层平均值
   </h1>
   <p>
    给定一个非空二叉树, 返回一个由每层节点平均值组成的数组.
   </p>
   <p>
    <strong>
     示例 1:
    </strong>
   </p>
   <pre><strong>输入:</strong>
    3
   / \
  9  20
    /  \
   15   7
<strong>输出:</strong> [3, 14.5, 11]
<strong>解释:</strong>
第0层的平均值是 3,  第1层是 14.5, 第2层是 11. 因此返回 [3, 14.5, 11].
</pre>
   <p>
    <strong>
     注意：
    </strong>
   </p>
   <ol>
    <li>
     节点值的范围在32位有符号整数范围内。
    </li>
   </ol>
  </div>
 </body>
</html>